The standard telephone consists of a base unit and a handset unit connected to each other by an electrical cord. The base unit itself is connected by another cord to a receptacle on a wall, telephone pole or a similar immovable structure to which the telephone network line extends. Therefore, the range of movement of the operator of the telephone is quite limited. Even when the cords connecting the handset unit to the base unit and the base unit to the wall are long, it can be cumbersome to move either the entire telephone around to make calls from different locations or to walk around with the handset unit once a call has been placed. The simple fact that there is always a continuous physical connection between the person making the phone call and the immovable wall or other fixed structure can be a great inconvenience.
The cordless telephone represents a significant improvement over the standard telephone. In the conventional cordless telephone, the base unit is still connected to the receptacle on the immovable wall or the like by a cord so that message signals from the telephone network line may be received and transmitted. However, the handset unit of the cordless telephone is an independently operative unit from which calls may be made and by which calls may be received with no physical connection to the base unit. Instead, the base unit and the handset unit of the cordless telephone communicate with each other over a communication channel established by the transmission and reception of electromagnetic waves, conventionally radio waves. The handset unit may then be taken to distances of up to 300 meters from the base unit, while still making and receiving telephone calls.
The handset unit has a transmitting/receiving system or transceiver and a loudspeaker in the earpiece and a microphone in the mouthpiece. In some cordless telephones, the base unit also has a loudspeaker and microphone either incorporated within the base unit itself or in an auxiliary standard telephone connectable to both the base unit and the outside telephone network line. When the base unit receives an incoming call, the base loudspeaker/microphone can be used to converse directly with the caller.
Two modes of operations are possible. In the telephone mode of operation, either the base unit or the handset unit is in communication with the outside telephone network line, and in the intercom mode of operation, the base unit and the handset unit are in communication with each other. This makes operation of the cordless telephone very convenient.
When such an intercom mode is available, there is the possibility that an incoming telephone call will appear when the cordless telephone is in the intercom mode. To announce the presence of the incoming call, both the handset unit and the base unit will ring. The handset unit conventionally rings by producing a ringing sound from its loudspeaker. When the handset operator is talking to the base operator, he is holding the handset unit with the loudspeaker directly next to his ear. The normal ringing sound could be unpleasant or painfully loud under these circumstances.
Prior art cordless telephones of this type have had a mode switch on the base unit which is actuated when an incoming call appears in the intercom mode to cause a changeover from the intercom mode to the telephone mode with the base unit in communication with the telephone network line. However, the operation of such prior art mode switches has been inconvenient and unduly complicated, leading to a likelihood of misactuation by those who are unfamiliar with cordless telephones in particular and electronic devices in general. It would be advantageous to provide a cordless telephone with an operation so simple that it is unnecessary to understand how it works in order to operate it successfully.
A further disadvantage of the described prior art cordless telephone is that only the base operator can answer the incoming telephone call since the mode switch is provided only on the base unit. This limits the flexibility of the cordless telephone.